Hello,
I am solving the Stokes equations on a MAC grid discretized by finite
differences using a DMSTAG object. I have tested the solver quite
extensively on manufactured problems and it seems to work well. As I am
still just trying to get things working and not yet worried about speed I
am using the following solver options:
-pc_type fieldsplit
-pc_fieldsplit_detect_saddle_point
-fieldsplit_0_pc_type lu
-fieldsplit_1_ksp_rtol 1.e-8
However I am now using this solver as an inner step of a larger code and
have run into issues. The code repeatedly solves the Stokes equations with
varying right hand sides coming from changing problem geometry (the solver
is a part of an overset grid scheme coupled to a level set method evolving
in time). After a couple timesteps I observe the following output when
running with -fieldsplit_1_ksp_converged_reason
-fieldsplit_1_ksp_monitor_true_residual:
Residual norms for back_fieldsplit_1_ solve.
0 KSP preconditioned resid norm 2.826514299465e-02 true resid norm
2.826514299465e-02 ||r(i)||/||b|| 1.000000000000e+00
1 KSP preconditioned resid norm 7.286621865915e-03 true resid norm
7.286621865915e-03 ||r(i)||/||b|| 2.577953300039e-01
2 KSP preconditioned resid norm 1.500598474492e-03 true resid norm
1.500598474492e-03 ||r(i)||/||b|| 5.309007192273e-02
3 KSP preconditioned resid norm 3.796396924978e-04 true resid norm
3.796396924978e-04 ||r(i)||/||b|| 1.343137349666e-02
4 KSP preconditioned resid norm 8.091057439816e-05 true resid norm
8.091057439816e-05 ||r(i)||/||b|| 2.862556697960e-03
5 KSP preconditioned resid norm 3.689113122359e-05 true resid norm
3.689113122359e-05 ||r(i)||/||b|| 1.305181128239e-03
6 KSP preconditioned resid norm 2.116450533352e-05 true resid norm
2.116450533352e-05 ||r(i)||/||b|| 7.487846545662e-04
7 KSP preconditioned resid norm 3.968234031201e-06 true resid norm
3.968234031200e-06 ||r(i)||/||b|| 1.403932055801e-04
8 KSP preconditioned resid norm 6.666949419511e-07 true resid norm
6.666949419506e-07 ||r(i)||/||b|| 2.358717739644e-05
9 KSP preconditioned resid norm 1.941522884928e-07 true resid norm
1.941522884931e-07 ||r(i)||/||b|| 6.868965372998e-06
10 KSP preconditioned resid norm 6.729545258682e-08 true resid norm
6.729545258626e-08 ||r(i)||/||b|| 2.380863687793e-06
11 KSP preconditioned resid norm 3.009070131709e-08 true resid norm
3.009070131735e-08 ||r(i)||/||b|| 1.064586912687e-06
12 KSP preconditioned resid norm 7.849353009588e-09 true resid norm
7.849353009903e-09 ||r(i)||/||b|| 2.777043445840e-07
13 KSP preconditioned resid norm 2.306283345754e-09 true resid norm
2.306283346677e-09 ||r(i)||/||b|| 8.159461097060e-08
14 KSP preconditioned resid norm 9.336302495083e-10 true resid norm
9.336302502503e-10 ||r(i)||/||b|| 3.303115255517e-08
15 KSP preconditioned resid norm 6.537456143401e-10 true resid norm
6.537456141617e-10 ||r(i)||/||b|| 2.312903968982e-08
16 KSP preconditioned resid norm 6.389159552788e-10 true resid norm
6.389159550304e-10 ||r(i)||/||b|| 2.260437724130e-08
17 KSP preconditioned resid norm 6.380905134246e-10 true resid norm
6.380905136023e-10 ||r(i)||/||b|| 2.257517372981e-08
18 KSP preconditioned resid norm 6.380440605992e-10 true resid norm
6.380440604688e-10 ||r(i)||/||b|| 2.257353025207e-08
19 KSP preconditioned resid norm 6.380427156582e-10 true resid norm
6.380427157894e-10 ||r(i)||/||b|| 2.257348267830e-08
20 KSP preconditioned resid norm 6.380426714897e-10 true resid norm
6.380426714004e-10 ||r(i)||/||b|| 2.257348110785e-08
21 KSP preconditioned resid norm 6.380426656970e-10 true resid norm
6.380426658839e-10 ||r(i)||/||b|| 2.257348091268e-08
22 KSP preconditioned resid norm 6.380426650538e-10 true resid norm
6.380426650287e-10 ||r(i)||/||b|| 2.257348088242e-08
23 KSP preconditioned resid norm 6.380426649918e-10 true resid norm
6.380426645888e-10 ||r(i)||/||b|| 2.257348086686e-08
24 KSP preconditioned resid norm 6.380426649803e-10 true resid norm
6.380426644294e-10 ||r(i)||/||b|| 2.257348086122e-08
25 KSP preconditioned resid norm 6.380426649796e-10 true resid norm
6.380426649774e-10 ||r(i)||/||b|| 2.257348088061e-08
26 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
6.380426653788e-10 ||r(i)||/||b|| 2.257348089481e-08
27 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
6.380426646744e-10 ||r(i)||/||b|| 2.257348086989e-08
28 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
6.380426650818e-10 ||r(i)||/||b|| 2.257348088430e-08
29 KSP preconditioned resid norm 6.380426649795e-10 true resid norm
6.380426649518e-10 ||r(i)||/||b|| 2.257348087970e-08
30 KSP preconditioned resid norm 6.380426652142e-10 true resid norm
6.380426652142e-10 ||r(i)||/||b|| 2.257348088898e-08
31 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426646799e-10 ||r(i)||/||b|| 2.257348087008e-08
32 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426648077e-10 ||r(i)||/||b|| 2.257348087460e-08
33 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426649048e-10 ||r(i)||/||b|| 2.257348087804e-08
34 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426648142e-10 ||r(i)||/||b|| 2.257348087483e-08
35 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426651079e-10 ||r(i)||/||b|| 2.257348088522e-08
36 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650433e-10 ||r(i)||/||b|| 2.257348088294e-08
37 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426649765e-10 ||r(i)||/||b|| 2.257348088057e-08
38 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650364e-10 ||r(i)||/||b|| 2.257348088269e-08
39 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650051e-10 ||r(i)||/||b|| 2.257348088159e-08
40 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426651154e-10 ||r(i)||/||b|| 2.257348088549e-08
41 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650246e-10 ||r(i)||/||b|| 2.257348088227e-08
42 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650702e-10 ||r(i)||/||b|| 2.257348088389e-08
43 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426651686e-10 ||r(i)||/||b|| 2.257348088737e-08
44 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650870e-10 ||r(i)||/||b|| 2.257348088448e-08
45 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426651208e-10 ||r(i)||/||b|| 2.257348088568e-08
46 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426651441e-10 ||r(i)||/||b|| 2.257348088650e-08
47 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650955e-10 ||r(i)||/||b|| 2.257348088478e-08
48 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650877e-10 ||r(i)||/||b|| 2.257348088451e-08
49 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426651240e-10 ||r(i)||/||b|| 2.257348088579e-08
50 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426650534e-10 ||r(i)||/||b|| 2.257348088329e-08
51 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426648615e-10 ||r(i)||/||b|| 2.257348087651e-08
52 KSP preconditioned resid norm 6.380426652141e-10 true resid norm
6.380426649523e-10 ||r(i)||/||b|| 2.257348087972e-08
53 KSP preconditioned resid norm 6.380426652140e-10 true resid norm
6.380426652601e-10 ||r(i)||/||b|| 2.257348089061e-08
54 KSP preconditioned resid norm 6.380426652125e-10 true resid norm
6.380427512852e-10 ||r(i)||/||b|| 2.257348393411e-08
55 KSP preconditioned resid norm 6.380426651849e-10 true resid norm
6.380603444402e-10 ||r(i)||/||b|| 2.257410636701e-08
56 KSP preconditioned resid norm 6.380426646751e-10 true resid norm
6.439925413105e-10 ||r(i)||/||b|| 2.278398313542e-08
57 KSP preconditioned resid norm 6.380426514019e-10 true resid norm
2.674218007058e-09 ||r(i)||/||b|| 9.461186902765e-08
58 KSP preconditioned resid norm 6.380425077384e-10 true resid norm
2.406759314486e-08 ||r(i)||/||b|| 8.514937691775e-07
59 KSP preconditioned resid norm 6.380406171326e-10 true resid norm
3.100137288622e-07 ||r(i)||/||b|| 1.096805803957e-05
Linear back_fieldsplit_1_ solve did not converge due to
DIVERGED_BREAKDOWN iterations 60
Any advice on steps I could take to elucidate the issue would be greatly
appreciated. Thanks so much for any help in advance!
Best,
Colton Bryant
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